Optical fiber ribbon cables are well known for the transmission of optical signals. Use of optical cables, including optical fiber ribbon cables, has generally been limited to long-haul trunking installations where the improved transmission characteristics of the optical fibers justify the greater expense and difficulty associated with their manufacture and installation. As the demands on communication media continue to increase, the advantages of using optical cable for transmission of signals across shorter distances or, for interconnecting local devices, continues to grow. Unfortunately, the costs associated with the production of optical fiber cable assemblies, and in particular with the installation of connectors on optical fiber ribbon cables, continue to limit the wide spread application of optical fiber transmission media for these applications.
Traditionally, a single fiber optical cable is assembled by coating an optical fiber with a buffer layer and then encasing the buffered optical fiber within a Kevlar.RTM. sheath that provides tensile strength and a vinyl outer jacket that serves as an environmental shield. Multi-fiber optical cables are assembled in a similar manner by bundling multiple buffered optical fibers within the center of a Kevlar.RTM. sheath and corresponding outer jacket. The difficulty with a multi-fiber bundled optical cable is in providing an economic, convenient and reliable system for installing a connector on the ends of the optical fibers so as to provide a finished fiber optic cable assembly.
As an alternative to a multi-fiber bundled optical cable, optical fiber ribbons have been developed in which multiple optical fibers are aligned and maintained in a planar configuration. U.S. Pat. No. 3,920,432, issued to Smith describes an early method of fabricating an optical fiber ribbon cable in which a plurality of glass optical fibers are carried by a grooved holder with a plurality of spacing fibers of triangular cross-section continuously fed into the spaces between adjacent optical fibers in the holder. The spacing fibers are then melted to secure the optical fibers within the holder. The advantage of this technique is that the optical fibers are accurately aligned within the holder, thereby aiding in the ability to easily interface the fiber optic ribbon with an optical connector. The disadvantage is that this technique limits the mechanical performance of the fiber optic ribbon by requiring that the holder be provided for the entire length of the ribbon and that the holder have sufficient structural integrity to accurately maintain the positioning of the optical fibers within the holder. In addition, the requirement that the fiber optic ribbon be heated in order to melt the triangular-type spacing fibers to secure the optical fibers within the holder subjects the fiber optic ribbon to thermal stress.
U.S. Pat. No. 4,289,558 issued to Eichenbaum et al. and U.S. Pat. No. 4,980,007, issued to Ferguson describe improved methods of fabricating a fiber optic ribbon in which buffered optical fibers are positioned adjacent one another in a planar orientation and then sandwiched between the adhesive layers of a pair of thin binding tapes. The resulting fiber optic ribbon is then encased in Kevlar.RTM. fibers and a plastic sheath, for example, to provide tensile strain relief and environmental protection for the optical fibers. In this technique, the alignment of the optical fibers within the ribbon is created and maintained by relying on the dimensional characteristics of the buffer layer surrounding the optical fibers and then abutting adjacent fibers so as to achieve a uniform spacing across a cross-sectional width of the fiber optic ribbon. While these techniques provide a clear manufacturing advantage to the technique disclosed by Smith in U.S. Pat. No. 3,920,432, the problems which are created by utilizing these techniques are an increased difficulty in attaching, aligning and installing optical connectors on the ends of the fiber optic ribbon in order to create a finished fiber optic ribbon cable assembly.
Numerous optical connectors have been developed to aid in the connection and splicing of fiber optic ribbons. Examples of connectors which are designed to terminate an end of a fiber optic ribbon are shown and described in U.S. Pat. No. 3,864,018, issued to Miller, U.S. Pat. No. 4,793,683, issued to Cannon, Jr., et al., and U.S. Pat. No. 5,309,537, issued to Chun, et al. In contrast, U.S. Pat. No. 3,871,935, issued to Cloge, et al. and European Patent Publ. No. 0 613 031 81 both describe methods for encapsulating a middle portion of a fiber optic ribbon within an optical connector assembly that is then severed in half to form opposed ends of a pair of optical connectors. In both of these references, the protective jacket and buffer surrounding the optical fibers are chemically removed in a middle portion of the ribbon and the resulting bare optical fibers are positioned within an encapsulating mold into which a bonding material is injected to secure the optical fibers. Once secured, the molded assembly is divided in half along a plane perpendicular to the axis of the optical fibers, thereby exposing ends of the fibers which can be polished for alignment and/or abutment to other optical fiber ends. The advantages of these encapsulation connector techniques are that they involve less manipulation and mechanical stress of the optical fibers than the technique taught by Smith. The disadvantages are that the stripping step subjects the optical fibers to potential damage and that the alignment of optical fibers in the molded assembly is not certain due to the potential movement of optical fibers during the encapsulating process. Additionally, this process is very labor intensive and not easily duplicated in the field where a ribbon cable has already been installed.
It would be desirable to provide a ribbon cable capable of easy field connectorization. Currently there are two primary multi-fiber connectors, AT & T's MAC.TM. connector and the MT.TM. connector made by U.S. Conec. The MAC.TM. connector made by AT & T is not designed to be field installable at all. The MT.TM. connector can be field installed, but not simply. When a field technician desires to insert an MT.TM. connector onto an existing ribbon cable, the technician cuts the ribbon cable. The insulation jacket surrounding the ribbon cable is typically slit longitudinally to allow the insulation jacket to be peeled back. If the ribbon cable is cut too deeply at this point, the optical fibers could be scratched and damaged. Any strengthening members in the ribbon cable must also be peeled back. After peeling back the insulation jacket and any strengthening members that may be present, the technician is left with a fiber ribbon comprising a plastic ribbon coating encapsulating a series of optical fibers.
The tool used to strip the plastic ribbon coating from the optical fiber is usually a hot blade stripper. This tool heats up the entire end of the ribbon which is being stripped and then has two blades that come towards one another to cut the ribbon coating and pull the coating off of the fibers. This step often causes damage to the fibers because it is very easy to cut too deeply with the blades and therefore damage the fibers. Once the fibers are exposed and are cleaned with alcohol to remove any remaining coating residue or particles, the connector must be correctly filled with the appropriate amount of adhesive. Then the fibers are manually inserted through holes in the connector. Once this is done, the adhesive must be cured to secure the fibers on the connector.
While fiber optic ribbon cables have expanded the use of optical fibers, the existing methods of stripping and connectorizing fiber optic ribbon cables are very labor intensive and subject the optical fibers to potential damage due to the difficulty in stripping the protective jacket and buffer. Attempting to thread the optical fibers through the holes of a connector is also a very tedious task. If even a single fiber is broken in either part of this process, a new cut of the ribbon cable must be made and the entire process must be redone. Consequently, it would be desirable to provide an improved system for stripping and connectorizing fiber optic ribbon cables subsequent to cable fabrication.